Syndicated columnist Robert Novak announced his immediate retirement today, telling the Chicago Sun-Times that his prognosis from a brain tumor is "dire.

The details are being worked out with the doctors this week, but the tentative plan is for radiation and chemotherapy," Novak told the newspaper.

Novak, 77, was cited last month for hitting a homeless pedestrian while driving in downtown Washington in his black Corvette. Chased down a block away by a bicylcist, Novak said he had no idea he had hit the man.

He was also the first journalist to reveal the identity of former CIA operative Valerie Plame. Novak's column on Plame in 2003 unleashed a federal investigation that brought down I. Lewis "Scooter" Libby, chief of staff to Vice President Dick Cheney, and seriously damaged the reputation of Deputy Secretary of State Richard Armitage and White House political maestro Karl Rove for leaking her name to other journalists. The sanctioned leak was an attempt to discredit Plame's husband, former U.S. Ambassador Joe Wilson, a public critic of the war in Iraq.

For more than 50 years, Novak has been part of the fabric of Washington journalism and politics. He teamed up with Rowland Evans in 1963 to write a column that was first distributed by Publishers Newspaper Syndicate on May 15, 1963, and after Evans retired, he kept going solo. He was co-host of CNN's Crossfire for 25 years before leaving in 2005 -- after storming off the set -- to work as a commentator on Fox News